Abstract: It has been found that high pressur,high temperature and shock wave during cavitaing bubble collapse induced by ultrasonic signal have evident effect at the process of ultrasonic degrading organic liquor.The investigation indicates that we can find out the best pressure and frequency for obtaining the maximal degrading efficiency in the range of steady cavitation.Cavitating bubble can keep on a steady vibration in a given original radius.The maximum of cavitation can be obtained at the best original radius.Degrading efficiency has an inverse ratio relationship with viscosity.The investigation also indicates that dual-frequency ultrasonic signal is much more efficient than single- frequency ultrasonic signal,the result is in agreement with the experiment basically.